The broad objectives of this project are (1) to study the effects of a variety of commonly used drugs on schedule-controlled behavior, with particular emphasis on diminished effects (tolerance) that often occur with chronic administration, and (2) to study the extent to which characteristics of the behavior itself influence the development and loss of tolerance to a particular drug, as well as cross-tolerance to another drug which may or may not be pharmacologically related. Because the effects of acutely administered drugs depend on the ways in which behavior is controlled by the environment, it is to be expected that development and loss of tolerance also depend on features of behavior. Our experiments will study effects of different classes of drugs on responding in different behavioral situations. We will study effects of chronically administered drugs on behavior maintained by food or water presentation and behavior suppress by presentation of an aversive event (punishment). We will specifically include schedules under which drug-produced changes in responding can result in marked changes in the overall frequency of the event maintaining behavior.